Use atomic operation to read the length of a fixed array.

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
 
 #include "src/v8.h"
@@ skipping 2608 matching lines @@
       WeakCell* cell = WeakCell::cast(detached_contexts->get(i + 1));
       if (mark_sweeps > 3) {
         PrintF("detached context 0x%p\n survived %d GCs (leak?)\n",
                static_cast<void*>(cell->value()), mark_sweeps);
       }
     }
   }
   if (new_length == 0) {
     heap()->set_detached_contexts(heap()->empty_fixed_array());
   } else if (new_length < length) {
-    heap()->RightTrimFixedArray<Heap::FROM_MUTATOR>(*detached_contexts,
-                                                    length - new_length);
+    heap()->RightTrimFixedArray<Heap::CONCURRENT_TO_SWEEPER>(
+        *detached_contexts, length - new_length);
   }
 }
 
 
 bool StackLimitCheck::JsHasOverflowed() const {
   StackGuard* stack_guard = isolate_->stack_guard();
 #ifdef USE_SIMULATOR
   // The simulator uses a separate JS stack.
   Address jssp_address = Simulator::current(isolate_)->get_sp();
   uintptr_t jssp = reinterpret_cast<uintptr_t>(jssp_address);
   if (jssp < stack_guard->real_jslimit()) return true;
 #endif  // USE_SIMULATOR
   return GetCurrentStackPosition() < stack_guard->real_climit();
 }
 
 
 bool PostponeInterruptsScope::Intercept(StackGuard::InterruptFlag flag) {
   // First check whether the previous scope intercepts.
   if (prev_ && prev_->Intercept(flag)) return true;
   // Then check whether this scope intercepts.
   if ((flag & intercept_mask_)) {
     intercepted_flags_ |= flag;
     return true;
   }
   return false;
 }
 
 } }  // namespace v8::internal